1. Field of the Invention
In many situations, it is desirable that cells, such as microorganisms, plant cells, mammalian tissues, or the like be able to withstand elevated osmotic pressures. For a variety of reasons it may be desirable or necessary for cells to grow in or tolerate an environment having enhanced osmolarity. For example, where hybrid DNA technology is involved, it could be desirable to use a relatively concentrated nutrient medium, where the constituents of the nutrient medium result in an elevated osmotic pressure. With plants, it will be desirable to be able to employ low grade waters having elevated saline content. Alternatively, many soils due to continued irrigation or other reasons have increased their salinity. In both situations, the ability for plant cells to grow in an environment having enhanced salinity would be very useful in increasing the amount of arable land.
It would therefore be desirable to provide ways to permit cells to grow in or tolerate an environment of enhanced osmolarity. By having such cells, one could greatly expand the conditions under which cells can be grown.
2. Description of the Prior Art
Csonka, Genetic Engineering of Osmoregulation (1980) eds. Rains, Valentine and Hollaender, Plenum Publising Corp., New York, describes the role of L-proline in response to osmotic stress. That article and the references contained therein, particularly the references referred to on pages 35-36 should be noted. Condamine, Annales de Institut Pasteur, Paris 120, 126-142 (1972) indicates that proline over-production may be a result of alteration of the first enzyme of the proline biosynthetic pathway. Csonka (1981) Mol. Gen. Genet. 182:82-86 describes the isolation of Salmonella typhimurium TL126 including mutant proBA genes on an F'-plasmid which provide for the overproduction of proline and confer osmotic tolerance.